In certain applications, there is a need to transfer alternating current (AC) power from an AC power source to a load in a circuit in which there is a very large direct current (DC) voltage differential between the AC power source and the load. A transformer is often used in such applications for isolating the AC power source from the load.
For example, in an x-ray tube, a cathode is electrically isolated from an anode. A power supply can provide a DC voltage differential between the cathode and the anode of typically about 4-150 kilovolts (kV). This very large voltage differential between the cathode and the anode provides an electric field for accelerating electrons from the cathode to the anode. The cathode can include a cathode element for producing electrons. The cathode element is a load in the circuit. A power supply can also provide an alternating current to the cathode element in order to heat the cathode element for electron emission from the cathode element. For instance, the alternating current may be supplied by a separate power supply or an AC power source embedded with the DC power supply.
There is a very large DC voltage differential between the AC power source and the cathode element, such as about 4-150 kilovolts (kV). The AC power source can be part of a low voltage side of the circuit and the cathode element can be part of a high voltage side of the circuit. A transformer is normally used to isolate the AC power source from the cathode element, or in other words the transformer can isolate the low voltage side of the circuit from the high DC voltage side of the circuit.
Due to the very high DC voltage differential between the AC power source and the load, arcing can occur at the transformer between the wires on the low voltage side of the transformer and the wires on the high voltage side of the transformer. Such arcing can reduce or destroy the DC voltage differential and thus reduce or destroy cathode electron emission and electron acceleration between the cathode and the anode. Although increased wire insulation can help to reduce this problem, defects in the wiring insulation can result in arcing. Also, due to space constraints, especially in miniature x-ray tubes, increased wiring insulation may not be feasible.